Disclosed herein is an invention residing in the art of braking systems and more particularly in braking systems for aircraft. It has been known for many years to utilize a plurality of brake disks, alternately splined to the wheel and axle of an aircraft, to impart a braking force to the aircraft. Such braking is achieved by forcing the alternately splined disks into contacting engagement with each other. Such disks have been found to be quite satisfactory in braking systems but, unfortunately, the same have a tendency to wear with repetitive braking action and, with a large number of disks in a stack, a small amount of wear in each disk results in a large amount of aggregate wear for the system. Consequently, adjustments need to be made to compensate for this wear such that brake pedal travel or brake piston extension and the force imparted to the brake are consistent with braking effort notwithstanding the wear experienced by the brake disk stack. Of course, it is also desirable to provide such adjustment in order that maximum use of the disks of the brake disk stack may be achieved.
Heretofore, various approaches have been taken to achieve brake adjustment. Standard types of adjusters have included frictionally slidable units maintained upon a tube. Using such adjuster mechanisms, it has been found that for any given distance of brake travel or brake application, a variance of loads exists. The force required to overcome the frictional engagement between the slidable unit and the tube changes with successive brake applications such that the force versus displacement curves of such adjusters do not trace each other on successive brake applications. Consequently, as the brake disks wear, the amount of force dissipated in the adjustment step of brake application varies between applications.
Further, in the prior art brake adjusters of the type mentioned above, it has become apparent that there is a difference between the static and dynamic coefficient of friction existing between the tube and the slidable unit. Upon the initial application of brake pressure, the amount of travel experienced by the return mechanism is to take up what is known as the "built-in clearance." The next minute portion of travel is that compensating for brake wear experienced during the prior braking efforts. Following this, the force applied is that referred to in the art as the effective brake force or that actually causing the frictional interengagement between the alternately splined disks. The problem with the prior art teachings is that the static coefficient of friction between the slidable unit and the tube is normally greater than the dynamic coefficient of friction therebetween. Consequently, the force applied to effectuate movement of the standard adjuster must be sufficient to overcome the static and dynamic coefficients of friction as well as the force imparted by the return spring of the spring follower characterizing such adjusters. Should the dynamic coefficient of friction be substantially less than the static coefficient of friction, and the spring of the spring follower be sufficiently strong, the spring follower may return the adjuster to a point where there is no longer a "built-in clearance." The result is a locked brake or a loss of "built-in clearance" for subsequent brake applications, the brakes then being extremely sensitive.
The instant invention relates to a brake adjuster apparatus which circumvents problems of the prior art teachings in a cost effective manner. Particularly, the invention disclosed includes a broaching technique wherein a tubular member is broached by an extendable shaft connected to the brake pressure plate. It has been found that such an apparatus circumvents the frictional problems inherent in the prior art teachings mentioned hereinabove. Certain approaches have been taken in the prior art to achieve a grooving or scoring of a member in a return mechanism to achieve the desired adjustability. Such teachings are found in U.S. Pat. No. 2,888,109, wherein tracks are furrowed or grooved into a sleeve; U.S. Pat. No. 3,957,146, wherein there is an axial cutting of an adjustment member; and U.S. Pat. No. 4,010,828, wherein multiple concentric tubes are axially cut. It will be apparent from the accompanying detailed description of the preferred embodiment that the invention disclosed herein provides advantages over these prior art teachings and over the teachings of the art of frictional engagement of extendable members in a brake adjuster.